linux-kernel - Re: [for-next][PATCH 6/8] ftrace: Prevent RCU stall on PREEMPT

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Message-ID: <b95f7a3d-429a-3564-fc9e-fa05d1d551df@igalia.com>
Date:   Wed, 14 Dec 2022 12:53:04 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [for-next][PATCH 6/8] ftrace: Prevent RCU stall on
 PREEMPT_VOLUNTARY kernels

On 14/12/2022 11:01, Steven Rostedt wrote:
> From: "gpiccoli@...lia.com" <gpiccoli@...lia.com>

Hi Steve, would be possible to use my full name here, like: Guilherme G.
Piccoli <gpiccoli@...lia.com> ?

Thanks,


Guilherme

> 
> The function match_records() may take a while due to a large
> number of string comparisons, so when in PREEMPT_VOLUNTARY
> kernels we could face RCU stalls due to that.
> 
> Add a cond_resched() to prevent that.
> 
> Link: https://lkml.kernel.org/r/20221115204847.593616-1-gpiccoli@igalia.com
> 
> Cc: Mark Rutland <mark.rutland@....com>
> Suggested-by: Steven Rostedt <rostedt@...dmis.org>
> Acked-by: Paul E. McKenney <paulmck@...nel.org> # from RCU CPU stall warning perspective
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
> Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  kernel/trace/ftrace.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index d04552c0c275..b8e374a372e5 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -4204,6 +4204,7 @@ match_records(struct ftrace_hash *hash, char *func, int len, char *mod)
>  			}
>  			found = 1;
>  		}
> +		cond_resched();
>  	} while_for_each_ftrace_rec();
>   out_unlock:
>  	mutex_unlock(&ftrace_lock);